Apparatus comprising an antenna element and a metal part

ABSTRACT

An apparatus including an antenna element; a metal part; a ground; and a filter connected between the metal part and the ground that has a frequency dependent impedance.

FIELD OF THE INVENTION

Embodiments of the present invention relate to an apparatus comprisingan antenna element and a metal part.

BACKGROUND TO THE INVENTION

A radio communications apparatus comprises an antenna element fortransmitting and/or receiving radio signals. It may also comprise ametal part, separate to the antenna element, that is provided for afunction unconnected with the operation of the antenna element. Themetal part may be, for example, an electromagnetic shield for shieldingof electronic components, a structural support element such as a chassisor frame, part of an integrated component such as battery cell etc.

The presence of the metal part may affect the operationalcharacteristics of the antenna element because of electro-magneticcoupling.

One approach to this problem is to electrically isolate the metal partto suppress electric currents flowing within the part. A disadvantage ofthis approach is that the metal part may become electro-staticallycharged.

Another approach to this problem is to ground the metal part.

BRIEF DESCRIPTION OF THE INVENTION

The inventors have realized that the grounding topology chosen for ametal part may affect the performance of the antenna element. Thisproblem is compounded if the antenna element is a multi-band antennaelement as a satisfactory solution for one band may be unsatisfactoryfor other bands. It would therefore be desirable to provide more designfreedom in creating an effective grounding topology for a metal part.

According to one embodiment of the invention there is provided anapparatus comprising: an antenna element; a metal part; a ground; and afilter connected between the metal part and the ground that has afrequency dependent impedance.

According to another embodiment of the invention there is provided amethod of assembling an apparatus comprising a radiating antennaelement, the method comprising: electrically interconnecting a metalpart, separate to the antenna element, and a ground via a filter thathas a frequency dependent impedance.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention reference will nowbe made by way of example only to the accompanying drawings in which:

FIG. 1A is a plan view of an apparatus that grounds a metal part via afilter 12 that has a frequency dependent impedance;

FIG. 1B is a side view of the apparatus; and

FIG. 1C is a perspective side-top view of the apparatus.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIGS. 1A, 1B and 1C illustrate an apparatus 10 that comprises an antennaelement 2, a metal part 20, a ground 18 and a filter 12 connectedbetween the metal part 20 and the ground 18 that has a frequencydependent impedance.

FIG. 1A is a plan view of the apparatus 10, FIG. 1B is a side view ofthe apparatus 10 and FIG. 1C is a perspective side-top view of theapparatus 10.

In the illustrated example, the antenna element 2 is a multi-band radiofrequency radiator element having operational bands including at least afirst frequency band of operation and a second, different, frequencyband of operation.

The ground plane 4 is provided by a printed wiring board (PWB) 4 whichextends under and adjacent to the antenna element 2 and also the metalpart 20. The metal part 20 is physically and functionally separate anddistinct from the antenna element 2 and typically performs some otherfunction. It may, for example, be decorative trimming, a battery casingor electromagnetic shielding or a support for a keypad or some othersupporting chassis element.

The metal part 20 is electrically connected at different points viaelectrical connectors 22 _(n) to a ground 18 provided by the underlyingground plane (PWB) 4. The electrical connectors 22 provide a galvanic dccurrent path from the metal part 20 to the ground 18. Although multipleconnectors are illustrated, in other embodiments a single connector maybe used.

At least one of the current paths between the metal part 20 and theground plane 4 incorporates a filter 12 that has a frequency dependentimpedance. The frequency dependent impedance is arranged to berelatively low at one or more of the operational bands of the antennaelement 2 and relatively high for the other operational band or bands ofthe antenna element 2.

The filter may operate as a band-stop filter in that it has a very highimpedance for one (or more) of the operational bands of the antennaelement 2 but not the other or other operational bands. It will beappreciated that filters other than band-stop filters may be used andthat any form of filter network may be appropriate.

In the illustrated example, the filter 12 is a parallel LC filter thatcomprises a capacitor 14 connected in parallel with an inductor 16between ground 18 and the metal part 20. The capacitor 14 and theinductor 16, in this example, are discrete components which have valueschosen so that the resonant frequency ω_(o) of the LC circuitcorresponds to the second frequency band of the antenna element 2. As isknown to those skilled in the art, the effective impedance of theparallel LC filter 12 becomes very large at the resonant frequencyω_(o)=(LC)^(−1/2). Consequently, at the resonant frequency (the secondfrequency band of the antenna element 2) the metal part 20 that isconnected to ground 18 via the filter 12 becomes decoupled from theground 18 because of the filter's very high impedance. However, at alower frequency (e.g. the first frequency band) the metal part 20remains electrically coupled to the ground 18 via the inductor 16.

The parallel LC filter 12 provides a permanent dc current path to groundfrom the metal part 20, which prevents electro-static chargeaccumulating at the metal part 20.

It will therefore be appreciated that the current paths to ground forthe first frequency band include current paths via the electricalconnectors 22 ₁, 22 ₂, 22 ₃ and 22 ₄. However, at the second, higher,frequency band the current paths to ground include paths via theelectrical connectors 22 ₂, 22 ₃ and 22 ₄ but do not include a path viathe electrical connector 22 ₁.

It will be appreciated that any number of electrical connectors 22 maybe used to provide separate current paths to the ground 18 provided bythe PWB 4 from the metal part 20 and that some, or all, of these currentpaths may include within them a filter 12. The same or different filtersmay be used in the respective current paths. The filters may, forexample, be band-stop filters with stops at the same or differentoperational frequency bands.

In some embodiments, the connectors 22 which are used to make electricalconnection between the ground 18 provided by the PWB 4 and the metalpart 20 may also be used to secure, that is fix, the metal part 20 tothe PWB 4. For example, the electrical connectors 22 may be provided byscrews that screw parts of the metal part 20 into grounded portions ofthe PWB 4.

Apparatus 10 may be any type of radio transmission or reception deviceor a module for such a device. It may for example be a personalelectronic device that is hand-portable such as, for example, a mobilecellular telephone.

The antenna element 2 may have operational bandwidths (low insertionloss S11) for different radio frequency bandwidths. As an example, thefirst frequency band of operation may include one or more of US-GSM 850(824-894 MHz) and EGSM 900 (880-960 MHz) and the second frequency bandof operation may include one or more of PCN/DCS1800 (1710-1880 MHz),US-WCDMA1900 (1850-1990), WCDMA2100 (Tx: 1920-19801 Rx: 2110-2180) andPCS1900 (1850-1990 MHz). These bands represent current cellulartelecommunication radio frequency bands. In other embodiments one orboth of the operational frequency bands may relate to other radiofrequency bands such as the band for Wireless Local Area Networking(WLAN) and Bluetooth or the bands for mobile radio or television.

In the illustrated example, the antenna element 2 is a monopole antennaelement—a Planer Inverted F Antenna (PIFA) that overlies an adjacentground plane 4. Although a particular monopole antenna is illustrated,other monopole antenna elements may be used. One type of monopole is aninverted F antenna (IFA). It typically does not overlie a ground plane.Another type of monopole is an external retractable monopole. It alsodoes not overlie a ground plane. Types of antenna elements other thanmonoples may also be used such as dipoles, slots, waveguides etc. Theantenna element 2 may be an element for an internal antenna asillustrated in FIGS. 1A, 1B and 1C or may be an element for an externalantenna.

Although embodiments of the present invention have been described in thepreceding paragraphs with reference to various examples, it should beappreciated that modifications to the examples given can be made withoutdeparting from the scope of the invention as claimed. For example,although the embodiments of the invention have been described for thesake of clarity as having a single metal part, it should be understoodthat this limitation is not a technical limitation and the apparatus 10may have multiple grounded metal parts each of which may have one ormore current paths to ground some or all of which may be via filternetworks.

Whilst endeavoring in the foregoing specification to draw attention tothose features of the invention believed to be of particular importanceit should be understood that the Applicant claims protection in respectof any patentable feature or combination of features hereinbeforereferred to and/or shown in the drawings whether or not particularemphasis has been placed thereon.

I claim:
 1. An apparatus comprising: an antenna element; a ground; ametal part having non-antenna related functionality and configured to benon-moveable relative to the ground; a plurality of conductiveconnections providing galvanic dc current paths between the metal partand the ground; and a further conductive connection comprising a filterelectrically interconnected between the metal part and the groundwherein the filter is a band-stop filter having a very high impedance ata particular frequency band.
 2. An apparatus as claimed in claim 1,wherein the filter comprises a parallel LC circuit.
 3. An apparatus asclaimed in claim 2, wherein the parallel LC circuit comprises discretecomponents.
 4. An apparatus as claimed in claim 1, wherein said furtherconductive connection is one of multiple conductive connections betweenthe metal part and the ground which incorporate a filter.
 5. Anapparatus as claimed in claim 1, wherein the conductive connectionnearest the antenna element comprises the filter.
 6. An apparatus asclaimed in claim 1, wherein the conductive connections are provided byconnectors that connect the metal part to a grounded printed wiringboard.
 7. An apparatus as claimed in claim 1, wherein the antennaelement is a monopole antenna element.
 8. An apparatus as claimed inclaim 1, wherein the antenna element is positioned adjacent a groundplane that provides the ground.
 9. An apparatus as claimed in claim 1,wherein the antenna element is a multi band antenna element having afirst frequency band of operation and a second, different, frequencyband of operation.
 10. An apparatus as claimed in claim 9, wherein thefilter is tuned to the second frequency band.
 11. An apparatus asclaimed in claim 9, wherein the filter is a band-stop filter having avery high impedance at the second frequency band.
 12. An apparatus asclaimed in claim 1, wherein the metal part is any one of a supportingchassis, an electromagnetic shield, a frame, a component part, adecorative trimming, a battery casing or a support for a keypad.
 13. Anapparatus as claimed in claim 1 embodied as a module for a radiocommunication device or embodied as a radio communication device.
 14. Apersonal electronic device incorporating the apparatus as claimed inclaim
 1. 15. A method comprising: providing an antenna element; andelectrically interconnecting a metal part having non-antenna relatedfunctionality and a ground via a filter and via a plurality ofconductive connections to provide galvanic dc current paths between themetal part and the ground, wherein the metal part is configured to benon-moveable relative to the ground and wherein the filter is aband-stop filter having a very high impedance at a particular frequencyband.
 16. An apparatus as claimed in claim 4, wherein the apparatuscomprises a plurality of separate filters having frequency dependentimpedances and a plurality of the conductive connections provides aseparate current path to ground via the plurality of separate filters.17. An apparatus as claimed in claim 1 wherein the filter provides apermanent direct current path to ground from the metal part.
 18. Themethod according to claim 15 wherein providing an antenna elementcomprises providing a multi band antenna element having a firstfrequency band of operation and a second, different, frequency band ofoperation.
 19. The method according to claim 15 wherein saidelectrically interconnecting comprises electrically interconnecting themetal part and the ground via a plurality of conductive connectionswhich incorporate a filter.
 20. An apparatus as claimed in claim 15wherein the antenna element is a multi band antenna element having afirst frequency band of operation and a second, different, frequencyband of operation, the band-stop filter has a very high impedance at thesecond frequency band of operation and is tuned to the second frequencyband of operation.